Heretofore, before a color print which comprises a color image as a halftone dot image formed on a print sheet as a final product is produced by a color printing press, it is customary to generate a proof for proofing colors with a printing proofer such as a color printer or the like as an image output device.
The printing proofer is used because it can produce a hardcopy comprising a color image on a proof sheet (recording sheet), i.e., a proof, easily a plurality of times in a short period of time without the need for plate films and presensitized plates (PS plates) as is the case with printing presses.
In order to form a proof color image on a proof sheet, image data depending on a device [printing mediums (inks, printing presses, sheets, etc.), photos, image sensors, CRTs, LEDs, etc.], e.g., CMYK (cyan, magenta, yellow, black) image data, is converted into colorimetric data as device-independent image data, e.g., Lab image data or XYZ image data mathematically compatible therewith, by a standard printing profile (four-dimensional look-up table) given by a manufacturer or the like. Thereafter, the colorimetric data is converted into device-dependent image data for a color printer, e.g., RGB (red, green blue) image data, by a printing proofer profile (hereinafter referred to as "proofer profile"), e.g., a printer profile (three-dimensional look-up table). Using the device-dependent image data, a proof with a color image formed on a proof sheet is generated by a color printer (also referred to as "proofing printer").
The colors of a print to be produced by the printing press can be simulated by the proof generated by the color printer, so that the colors can be confirmed before they are actually printed.
Actually, the color reproduction range of the printing press and the color reproduction range of the printing proofer are different from each other. Therefore, a range that cannot be reproduced by the printing proofer is achieved by linking the printing profile and the proofer profile according to gamut mapping (color reproduction range mapping).
When a proof whose colors correspond to those of a print as a target is outputted from the printing proofer using the profiles thus linked, if the proof does not have sufficient color agreement, then the device-dependent image data CMYK are subjected to fine gradation adjustments (tone curve adjustments) prior to using the linked profiles.
However, such fine gradation adjustments are tedious and time-consuming because it is not clear as to what and how color shifts have to be corrected, and are also problematic in that some color shifts cannot be corrected by fine gradation adjustments.
The present invention has been made in view of the above drawbacks. It is an object of the present invention to provide a color correcting method which is capable of equalizing the colors of a proof produced by a proofer with the colors of a print as a target easily, reliably, and more accurately.